1. Technical Field
The present invention relates to an image displaying apparatus in which the operating power supplied to the load is controlled in accordance with the presence and absence of horizontal and vertical synchronizing signals in a computer system.
2. Related Art
An image displaying device such as a monitor using a cathode ray tube is a peripheral device which makes it possible for a user to check and monitor the operating state of a computer system connected to the monitor. In the computer system, signals for a current operation are outputted to the image display device, and the signals are displayed on the screen by the image display device. In order to display the computer signals on the screen of the cathode ray tube by the image display device, there are utilized horizontal and vertical synchronizing signals.
The image display device generates horizontal deflecting magnetic fields in accordance with the horizontal synchronizing signals, and generates vertical deflecting magnetic fields in accordance with the vertical synchronizing signals. Electron beams shot by an electron gun are deflected by the horizontal and vertical deflecting magnetic fields in accordance with the image signals. Thus a computer system outputs data signals as well as the horizontal and vertical synchronizing signals.
Video power savings for a monitor circuit are achieved in accordance with version 1.0 of the display power management signaling (DPMS) standard, dated Aug. 20, 1993, supported by the Video Electronics Standards Association (VESA). The Video Electronics Standards Association is an international non-profit corporation that supports and sets industry-wide interface standards for personal computer, workstation, and computing environments. Members of the Video Electronics Standards Association include hardware, software, personal computer, display and component manufacturers, cable and telephone companies, and service providers.
Power saving modes of the display power management signaling standard may be classified into a power-on mode, a standby mode, a suspend mode, and a power-off mode. The power saving mode of the display monitor is controlled by the horizontal and vertical synchronizing signals supplied from a host supporting the power savings modes. A personal computer may be the host.
If both types of synchronizing signals are supplied from the host, the display monitor apparatus is operated in the power-on mode. In the power-on mode, a high level of electrical power is supplied to the display monitor apparatus, such that full operational use of the display monitor apparatus is possible.
When only the vertical synchronizing signal is fed from the host, the power supply mode of the display monitor apparatus becomes the standby mode, in which a first group of circuits are put into a reduced power state. Standby mode can save approximately 30% of the power required for power-on mode and allows the display monitor apparatus to change to power-on mode instantly, as soon as needed.
When only the horizontal synchronizing signal is supplied from the host, the display apparatus is put into the suspend mode, in which a second group of circuits are put into a reduced power state. Suspend mode saves more power than standby mode by powering off the cathode ray tube's main heater but requires up to approximately 5 seconds to change to power-on mode.
When no synchronizing signals are provided from the host, the display monitor apparatus is put into the power-off mode. In such a case, electrical power supplied to the display monitor apparatus is changed to a low level, such that the screen of the display monitor apparatus is blank. Power-off mode saves more power by turning power off to everything except the monitor's microprocessor.
Thus, the aforementioned display power management signaling standard, proposed by the Video Electronics Standard Association, is capable of managing monitor power for a current mode and capable of reducing the power consumption.
The computer system utilizing the display power management signaling (DPMS) standard is capable of managing the power supplied to respective sections of the computer based on the state of the use of the computer system. The computer system selectively outputs horizontal and vertical synchronizing signals in accordance with the power supply mode in accordance with the display power management signaling (DPMS) standard. The monitor operates under an on-state mode, a standby mode, a suspend mode or a power-off mode in accordance with the presence or absence of the horizontal and vertical synchronizing signals.
That is, when both the horizontal and vertical synchronizing signals are outputted, the monitor operates under the on-state mode or power-on mode. When the vertical synchronizing signals are outputted and the horizontal synchronizing signals are not outputted, the monitor operates under the standby mode. When the horizontal synchronizing signals are outputted and the vertical synchronizing signals are not outputted, the monitor operates under the suspend mode. When neither the horizontal nor vertical synchronizing signals are outputted, the monitor operates under the power-off mode.
When the monitor operates under the on-state mode, the power consumption in accordance with the display power management signaling (DPMS) standard is about 80-100 watts (W). Under the standby mode, it is about 65 W or less. Under the suspend mode, it is about 25 W or less. Under the power-off mode, it is about 5 W or less.
Also, there are systems in which the on-state mode and the standby mode are merged into a normal mode, so that the managing mode can be divided into the normal mode, the suspend mode and the power-off mode. This type of three-mode power system is different from the aforementioned four-mode power system described in version 1.0 of the display power management signaling (DPMS) standard, dated Aug. 20, 1993, and supported by the Video Electronics Standards Association (VESA).
In the case of the three-mode power system, the power consumption is defined as follows. Under the normal mode, the power consumption is 80-100 W. Under the suspend mode, it is about 15 W or less. Under the power-off mode, it is about 5 W or less.
As described above, in the monitor in which the power is managed in accordance with the system operating mode, the power supply mode is shifted in accordance with the presence or absence of the horizontal and vertical synchronizing signals. Therefore, when the mode is shifted from the standby mode or the normal mode to the suspend mode, the operating power is greatly fluctuated.
Due to the fluctuations of the operating power, there occurs a transition phenomenon in which the operating power is severely lowered. Due to this transition phenomenon, the power which is supplied to the load is steeply decreased, and a surge current is supplied to the load. As a result, malfunctions occur, and the life expectancy of the power supply unit is shortened.
Meanwhile, in the case where the shifting is accompanied by a small power variation like when the on-state mode is shifted to the standby mode or the suspend mode is shifted to the power off mode, the transition phenomenon occurs, but in this case, the power fluctuation is low. Therefore, in this case, the apparatus is not much affected.
Accordingly, I have discovered that it would be desirable to provide an improved circuit reducing the aforementioned transition phenomenon and reducing the occurrence of damages associated with the transition phenomenon.